Use linear version User#groups_with_developer_maintainer_project_access

app/models/user.rb

@@ -2168,12 +2168,7 @@ class User < ApplicationRecord
       project_creation_levels << nil
     end
 
-    if Feature.enabled?(:linear_user_groups_with_developer_maintainer_project_access, self, default_enabled: :yaml)
-      developer_groups.self_and_descendants.where(project_creation_level: project_creation_levels)
-    else
-      developer_groups_hierarchy = ::Gitlab::ObjectHierarchy.new(developer_groups).base_and_descendants
-      ::Group.where(id: developer_groups_hierarchy.select(:id), project_creation_level: project_creation_levels)
-    end
+    developer_groups.self_and_descendants.where(project_creation_level: project_creation_levels)
   end
 
   def no_recent_activity?

config/feature_flags/development/linear_user_groups_with_developer_maintainer_project_access.yml

----
-name: linear_user_groups_with_developer_maintainer_project_access
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68851
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/339436
-milestone: '14.3'
-type: development
-group: group::access
-default_enabled: false

spec/models/user_spec.rb

@@ -6246,19 +6246,7 @@ RSpec.describe User do
 
     subject { user.send(:groups_with_developer_maintainer_project_access) }
 
-    shared_examples 'groups_with_developer_maintainer_project_access examples' do
-      specify { is_expected.to contain_exactly(developer_group2) }
-    end
-
-    it_behaves_like 'groups_with_developer_maintainer_project_access examples'
-
-    context 'when feature flag :linear_user_groups_with_developer_maintainer_project_access is disabled' do
-      before do
-        stub_feature_flags(linear_user_groups_with_developer_maintainer_project_access: false)
-      end
-
-      it_behaves_like 'groups_with_developer_maintainer_project_access examples'
-    end
+    specify { is_expected.to contain_exactly(developer_group2) }
   end
 
   describe '.get_ids_by_username' do